Draft pull requests marked "Ready for Review" does not send notification

[phajnal-odevo]

Describe the bug
When a Pull request is created as a Draft pull request then marked as Ready for Review, it does not send any notification to Slack anymore. This was working on 30 Oct.
To Reproduce
Steps to reproduce the behavior:

1. Subscribe to Pull request events in Slack: /github subscribe owner/repo pulls
2. Create a Pull request as draft
3. Mark it as Ready for Review
4. No notification

Expected behavior
As it was working previously, I'm expecting the following notifications in Slack:

1. Pull request opened by ..
2. Pull request ready for review by ...
3. Review approved by ... on ... pull request
4. Pull request merged by ...

Additional context
Official integration between GitHub and Slack. Everything else is working, except the described scenario above.